feat(app-expo): env variants, local iOS prebuild, and About diagnostics

Align staging/production builds with APP_VARIANT bundle IDs, allow staging HTTP on iOS, add ios-prebuild scripts for TestFlight, and show connected API URL on About for non-production builds.

Co-authored-by: Cursor <cursoragent@cursor.com>

app-expo/.env.staging

@@ -1,2 +1,5 @@
-EXPO_PUBLIC_API_URL=http://1.15.29.57:8000/
-EXPO_PUBLIC_WS_URL=ws://1.15.29.57:8000/
+# 预发：关于页显示版本 + 后端地址；iOS Bundle ID org.brighteng.lifecho.staging
+APP_VARIANT=staging
+EXPO_PUBLIC_APP_VARIANT=staging
+EXPO_PUBLIC_API_URL=http://1.15.29.57:8000
+EXPO_PUBLIC_WS_URL=ws://1.15.29.57:8000